Surgical Anatomy of the Posterior Intermuscular Approach to the Brachial Plexus.

Background: First rib resection and scalenectomy is a well-established treatment option for thoracic outlet syndrome. The posterior approach is rarely used due to extensive muscle sacrifice resulting in significant procedural morbidity. In this paper, we report the surgical anatomy of modified and less-invasive muscle-sparing posterior approach. Methods: Eleven human cadavers were used in this study. With specific care to preserve muscles' integrity, the brachial plexus was exposed by dissecting through the posterior neck musculature. A muscular triangle was found under the trapezius muscle, which provided direct access to deeper structures. Four anatomical reference points were identified to denote a 3-dimensional space enclosing proximal brachial plexus. Results: A muscular triangle was found under the trapezius muscle in all cadavers. It was bordered infero-medially by rhomboid minor, supero-medially by splenius capitis, and laterally by levator scapula muscles. The inferomedial border (rhomboid) was 55 mm (48-80), superomedial border (splenius capitis) was 60.5 mm (42-89), and the lateral border (levator scapulae) was 99 mm (60-130). A consistent vein was present inside the triangle and could be used as an anatomical landmark. The 4 reference points were C5, T1 intervertebral foramina, transverse tubercle, and scalene tubercle of the first rib. Removal of the first rib could be performed without brachial plexus retraction. The latter was exposed from neural foramina to lateral border of the first rib. Conclusions: The posterior approach provides ample space to for exposure and manipulation with the first rib and proximal brachial plexus.